Energy dense source for pulse power applications and novel electromagnetic armor

ABSTRACT

A supercapacitor-like device is described that uses a porous, conductive foam as the electrodes. After the device is charged, an explosive wave front can be used to remove electrolyte from the metal foam. This creates a large net charge on each electrode, which will readily flow through a load placed across the electrodes. The removal of charge can potentially occur on a time scale of microseconds, allowing a supercapacitor to be used in pulsed power applications. The creation of this net charge requires significant energy, meaning this concept may also be suitable for removing kinetic energy from objects.

RELATED APPLICATIONS

This application claims the benefit of priority of International PatentApplication Serial No. PCT/US18/39869 filed 27 Jun. 2018 and U.S.Provisional Patent Application No. 62/525,299 filed 27 Jun. 2017.

INTRODUCTION

In a conventional capacitor, the charge is stored in two parallel metalplates, with a charge of +Q on one plate and −Q on the other plate. Thecharge storage ability of the device is measured by the capacitance, C,which is given by the relation Q=CV, where V is the voltage differencebetween the plates. If a dielectric with dielectric constant e is addedbetween the plates, the capacitance is increased by a factor of ε. Thecapacitance of the device can be expressed simply as C=A/4πs, where A isthe area of the metal plate as s is the separation between the charges.Typically, this separation is on the order of several microns. When anexternal load is connected between the electrodes, electrons then flowfrom the ground electrode to the positively charged electrode. Becausethe charge is stored as electrons in the metal, the device can respondrapidly to the connection of the load, with response time far shorterthan a microsecond, which is the relevant time scale for many of theenvisioned applications.

More recently, there has been much development of supercapacitors, whichare a modification to the conventional capacitor design. In asupercapacitor, the flat metal plates are replaced by high surface areacarbon or metal oxide materials, which increases the area by a factor of1000 or more. Secondly, the charge on an electrode is now balanced bythe formation of a charged layer within the liquid electrolyte thatinfuses throughout the electrode. This decreases the separation betweencharged to the order of a few nanometers, instead of microns. Thiscombination of increased surface area and decreased separation resultsin a device where the capacitance has increased by 6 or more orders ofmagnitude. This also implies that several orders of magnitude morecharge can be stored within the same volume with a supercapacitorcompared to a conventional capacitor. Instead of a microfarad beingviewed as a large capacitance, it is possible to make 5000F capacitorsthat fit into your hand.

A limitation to these supercapacitors is that the response time is notdetermined by the speed of the holes or electrons that are on theelectrodes, but the rate at which the ions in the electrolyte candiffuse away to remove the charge layer. This slow diffusion of the ionscauses the response time of a supercapacitor to be on the order ofmilliseconds to seconds, much slower than required for manyapplications.

SUMMARY OF THE INVENTION

In a first aspect, the invention provides an explosion-poweredsupercapacitor, comprising: first and second porous electrodesconnectable to a power source and resistive load (“connectable” meansable to be connected to the power source to generate a potential orconnected to the resistive load to allow discharge of thesupercapacitor); a first liquid electrolyte in contact with the firstporous electrode; a second liquid electrolyte in contact with the secondporous electrode; a separator disposed between the first and secondelectrolytes; an explosive charge, wherein at least the first or secondelectrodes are in compressive contact with the explosive charge.“Compressive contact” means that the explosive charge is disposed withrespect to the electrode such that the force of the explosion compressesthe electrodes and decreases the volume of electrolyte stored within theelectrodes.

An “explosion” has the conventional meaning. An explosion is a rapidrelease of stored chemical and/or mechanical energy. An explosionreleasing stored chemical energy may result in the generation andrelease of gases at high pressure and/or temperature. The explosive willgenerate a compressive wavefront, which can be propagated through airand/or a rigid structure.

Typically, the same electrolyte solution is used to fill thesupercapacitor and thus provide both the first and second liquidelectrolyte. When the device is uncharged, the compositions of theelectrolytes are typically the same. The amount of electrolyte ejectedfrom each electrode does not need to be balanced, but the closer tobalanced, the more energy can be obtained from the device.

In some embodiments, the supercapacitor comprises at least oneelectrolyte outlet. The at least one electrolyte outlet can be a singleoutlet through which flows the electrolyte ejected from both electrodes,or could be a plurality of outlets; for example, two outlets for theelectrolyte from the first electrode and two outlets for the electrolytefrom the second electrode. In some embodiments, the first and secondelectrodes are directly adjacent to the separator.

In a another aspect, the invention provides a method of generating anenergy pulse, comprising: providing a supercapacitor, comprising: firstand second porous electrodes connectable to a power source and aresistive load; a first liquid electrolyte in contact with the firstporous electrode; a second liquid electrolyte in contact with the secondporous electrode; a separator disposed between the first and secondelectrolytes; applying a potential between the first and second porouselectrodes; creating an explosion that compresses the electrodes andreduces the volume of each porous electrode and ejects electrolyte fromthe porous electrodes thus increasing the potential between theelectrodes and increasing the energy stored in the supercapacitor; andsubsequently discharging (at least a portion of) the energy stored inthe supercapacitor. Preferably, at least 0.01% of the chemical energy ofthe explosive charge is converted to electrical energy, more preferablyat least 0.05%, or at least 0.1%, or at least 1% and, although 100% istheoretically possible, in some embodiments a practical limit may be10%.

In some embodiments, the step of compressing is sufficiently fast suchthat at least 0.1% (or at least 0.5%, or at least 1.0%, or at least2.0%, or up to 20% or up to 10%) of the net charge contained in theelectrolyte within the electrodes is ejected with the electrolyte duringcompression. The net charge can be calculated from measuring the currentas a function of time when charging the supercapacitor.

In a further aspect, the invention provides a method of convertingchemical energy to electrical energy, comprising: wherein energy isinitially stored as chemical energy in an explosive charge; triggeringthe explosion to convert the chemical energy to kinetic energyassociated with an explosive wavefront; wherein the impact of thewavefront on the electrode transfers kinetic energy to an electrolyte ina supercapacitor having porous conductive electrodes; converting aportion of the transferred kinetic energy in the electrolyte toelectrical energy stored in the supercapacitor. This stored electricalenergy is then available for pulse power applications.

In a another aspect, the invention provides an armor panel, comprisingin sequence: a first armor plate, an anode, a first electrolyte, aporous insulating separator, a second electrolyte, a cathode, and asecond armor plate; and an electrical connection between the anode andcathode; and further comprising at least one outlet for the firstelectrolyte and the second electrolyte; and wherein the components areconnected such that, when a kinetic or conductive threat impacts ortravels through an armor plate, the first and second electrolyte areejected and a potential between cathode and anode is increased.

A conductive threat could be, for example, an explosively formedpenetrator. For a conductive threat, the compression of the electrodesleads to a high voltage, and the conductive threat contacts both ananode and cathode, current will flow through the conductive threat,which reduces its effectiveness. In the case of a kinetic threat (normaltank gun round), the compression of the electrodes and ejection of theelectrolyte is achieved using energy coming from the round, whichreduces its effectiveness.

The device can function with a single anode where the supercapacitor iselectrically isolated from the armor. Preferably, the panel contains twoanodes so that the cathode could be isolated in the interior of thedevice. In some embodiments, the cathode is shared with a second anodeand the armor panel further comprises a third electrolyte, a secondporous insulating separator, and a fourth electrolyte; all disposedbetween the first and second armor plates.

The invention also includes a method of reducing a conductive or kineticthreat using the armor panel described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of device operation.

FIGS. 2a-2c is another schematic illustration of the activation of thedevice. a) the uncharged device, b) the device after charging to about1V, which places large net charges on the metallic electrode componentand electrolyte within each electrode, and c) the device after explosivecompression and ejection of electrolyte, resulting in an unbalancedcharge on each metallic component. This charge is at large potentialdifference and is available for rapid discharge in pulse powerapplications.

FIG. 3 is a schematic illustration of a system for generating anelectrical pulse.

FIG. 4 illustrates the potential difference between the electrodes forejections of 1%. 0.1% and 0.01% (top to bottom).

FIG. 5 illustrates the energy stored for ejections of 1%. 0.1% and 0.01%(top to bottom).

FIG. 6 illustrates a supercapacitor that accompanies a calculatedexample.

FIG. 7 illustrates a supercapacitor that accompanies a calculatedexample of the invention.

FIG. 8 is a schematic illustration of an embodiment of the armorconcept.

FIG. 9 shows a charge-discharge curve from a typical device.

FIG. 10 shows a charge-discharge curve from a typical device.

FIG. 11 shows a voltage curve of the device before and after impact.

FIG. 12 shows a voltage curve of an uncharged device

FIG. 13 shows a voltage curve of a device with no electrolyte.

FIG. 14 shows a voltage spike as a function of impact.

FIG. 15 shows a voltage curve of a device having carbon nanotube (CNT)films as the porous electrodes.

DESCRIPTION OF THE INVENTION

The current invention speeds the removal of the ions in the chargelayer, allowing the large stored charge to rapidly flow through anexternal load.

The supercapacitor electrodes comprise a high surface area, conductive(typically metal) foam. The conductive foam may have a surface area of100 m²/g or higher, while preferably having a mass density of 1 g/cm³ orless. Surface area can be measured by gas adsorption (BET). Theconductive foam has an open pore structure. The pair of electrodes willthen be placed into an electrolyte solution, and the device chargeduntil the amount of charge is saturated at the operating voltage of theelectrolyte. For example, if the device has capacitance of 0.5F andoperating voltage of 2.5V, 1.25 C of charge will be on each electrode.Although there is a charge of 1.25 C on each electrode, there is acounter-balancing charge of 1.25 C within the electrolyte that isinfused into each electrode. So although there is a large charge storedon the conductive foam, from the exterior, the conductive foam appearsto have no charge.

To activate the device, an explosive charge, or other large impulse isapplied to each electrode to compress the foam. This will result in theexpulsion of the electrolyte from the foam as it crushes. The expulsionof the electrolyte will now lead to each electrode plus infusedelectrolyte system to have a large net charge. If a load is now placedacross the electrodes, a significant portion of the stored 1.25 C chargewill flow. Because the time to compress the electrode can be on theorder of a microsecond, the response time of the device can now also beon the order of a microsecond.

There is a need for a device capable of providing high power pulsedenergy. For example, lasers could use such a device. For manyapplications, the need is for a power source capable of a high number ofrepetitions, while other applications may only one or a limited numberof repetitions. As part of this invention, it is believed it is possibleto design a device using this invention that would be capable ofmultiple repetitions. For example, the supercapacitor device would befed into a chamber, where a chemical explosive is used to compress thedevice. After compression and discharge of the device, it is removedfrom the chamber, and a new device introduced. Alternatively, anelastic, compressible porous electrode could be used over multiplerepetitions where the explosion doesn't irreversibly alter theelectrode.

Compared to other devices for converting chemical energy into high powerelectrical pulses, this invention can provide high power electricalpulses with a much less complex design, and less infrastructure neededto provide the power pulse. The mechanism of action in this invention isvery distinct from the prior art. In some of the prior art, a seedcurrent is needed, which is not required here. Much of the prior artalso requires significant machining of the device, which is thendestroyed after a single use. Technologies that use seed currents oftenare very sensitive to the inductance of the load. Ferroelectric andferromagnetic technologies do not convert chemical energy intoelectrical energy, but instead use the explosive to disrupt theferroelectric or ferromagnetic domains. The device can then only releasethe energy stored in these domains, which is orders of magnitude lowerthan the energy available from chemical explosives.

The fundamental principal is shown in FIG. 1 (note that the separator isnot shown). FIG. 1 illustrates a supercapacitor is formed from a pair ofporous metallic electrodes 12, 12′ (shown in gray). The device ischarged, which places a large net charge on each of the metallicelectrodes (positive on one electrode 12′, negative on the other 12),with a counter net charge contained in the electrolyte that resideswithin each porous electrode. The net total charge on the electrode pluselectrolyte contained within the electrode is zero. The application of alarge, rapid, force either through an explosion or other mechanicalmeans expels electrolyte 15 from each electrode. This expulsion removespart of the net charge that was contained in the electrolyte. This leadsto each electrode plus electrolyte pairing to now have a net charge.Because the capacitance between the electrode plus electrolyte pairs isvery small, this net charge results in a very large potential differencebetween the electrodes, which also implies a large amount of storedelectrical energy, which results from the work done by the explosion inexpulsing the charged electrolyte.

Another schematic view of the inventive method is shown in FIGS. 2a-2c .FIG. 2a shows the capacitor in the uncharged state, where there is nocharge residing on the metallic component of either electrode (brown)while the net ionic charge in the electrolyte (blue) is zero. FIG. 2bshows the supercapacitor after it has been charged to approximately 1V.There is now a large charge in each of the metallic electrodecomponents, while there is a net charge of equal magnitude but oppositesign in the electrolyte within the electrode, resulting in zero netcharge on either half of the device. FIG. 2c then shows thesupercapacitor after the explosive compression of the electrodes. Thecompression decreases the amount of electrolyte that can be contained ineach electrode, and as the electrolyte is ejected it carries some of thenet charge in that portion of the electrolyte. However, the compressiondoes not alter the amount of charge contained in the metallic componentof each electrode. This results in each half of the device now having alarge net charge. This net charge produces a large potential differenceacross the electrodes. If these electrodes are now connected across aload, a very large current can flow, providing the pulse power response.

The overall flow of energy in the device is:

-   -   1. Energy is initially stored as chemical energy of the        explosive    -   2. Triggering the explosion converts the chemical energy to        kinetic energy associated with the explosive wavefront    -   3. The impact of the wavefront on the electrode transfers        kinetic energy to the electrolyte    -   4. The kinetic energy of the moving net charge in the        electrolyte is converted to electrical energy stored by the        charge on the metallic electrode components.        This stored electrical energy is then available for pulse power        applications.

Typically, the amount of total charge needed in a pulse powerapplication is relatively low. For example, a current of 100 kA thatflows for 10 μsec only requires 1 C of charge to be stored in thedevice. This amount of charge is small by supercapacitor standards where10,000 C can be stored in a handheld device. This implies that only asmall fraction of the charge in the electrolyte must be ejected for thedevice to function as a pulse power source. The second is that thewavefront from the explosive can compress the electrode layer in a fewmicroseconds or less. It is the speed and energy of this explosivewavefront that causes the charge in the electrolyte to be ejectedrapidly from the electrode, which is responsible for the conversion ofthe kinetic energy from the explosion into the electrical energyreleased from the device.

FIG. 3 is a schematic illustration of a system for generating anelectrical pulse. An explosive is disposed in compressive contact withat least one porous electrode. The device includes current collectors B,C, and porous conductive electrodes F, G that are separated by separatorE. Initially, a potential is established by power source A. After theexplosive is discharged, the resulting wavefront compresses thesupercapacitor (reducing the length I) and forces electrolyte (carryingopposite charge from opposing sides of the separator) out of the volumeof the supercapacitor (volume is defined by H×I×Z (where Z is indirection perpendicular to page)). Thus generating a very high potentialbetween electrodes G and F that can be discharged as an electrical pulsethrough load D.

The various components are known. The porous, conductive electrodes canbe any of the known electrode materials such as carbon-based compositematerials with materials such as carbon nanotubes and graphene; metaloxides (e.g., MnO₂, RuO₂); conductive polymers, mixtures of thesematerials, preferably porous metals such as a porous nickel foam. Someof these such as the conductive polymer composites can be elastic. Theporous electrode should have connective porosity so that electrolyte isexpressed from the electrodes by the wavefront. The electrolyte is asolvent with dissolved chemical(s). The solvent can be water or anorganic solvent.

Preferably, the separator is in contact with the electrodes. Thisconfiguration helps convey the stress needed to compress the electrodes.In some embodiments, the explosion pushes the first electrode from oneside; the first electrode is then pushed against the separator, whichthen pushes against the second electrode.

A model to understand the basic function of the proposed device has beendeveloped, making assumptions about composition of the electrode, andthe fraction of the net charge ejected with the electrolyte duringcompression. The results show that even if less than 1% of the netcharge in the electrolyte is ejected from the electrode, the voltageacross the device could approach or exceed several thousand volts.

There are several factors to notice about this concept. First is thatthe amount of total charge needed in a pulse power application isrelatively low. A current of 100 kA that flows for 10 μsec only requires1 C of charge to be stored in the device. This amount of charge is smallby supercapacitor standards where 10,000 C can be stored in a handhelddevice. This implies that only a small fraction of the net charge of theelectrolyte held within the electrode must be ejected for thedevelopment of large voltage across the device.

As shown below, we developed a model to calculate the expectedperformance of such a device. The key inputs to this model include theelectrode initial porosity and thickness, and the initial surface area.Other key inputs include the electrode thickness after the crush, thefinal separation between the electrodes, and the fraction of the netcharge that is removed during the crushing event. This model assumed thepores are initially cylindrical, but become flattened as the electrodeis crushed. The total number of pores did not change. The crushingreduces the surface area, but this will be shown to be negligible. FIG.4 shows the potential difference between the two electrodes as afunction of the final separation between the electrodes. The electrodesare crushed 75% (C=0.75), and the fraction of the net electrolyte chargethat is ejected is varied (F=1%, 0.1%, 0.01%).

FIG. 5 shows the stored energy as a function of the final separationbetween the electrodes. The electrodes are crushed 75% (C=0.75), and thefraction of the net electrolyte charge that is ejected is varied (F=1%,0.1%, 0.01%). As shown in the figure, if even as little as 1% of the netcharge in the electrolyte is removed, the device can contain from 10 kJto more than 1 MJ. All this stored electrical energy comes from theconversion of the mechanical energy of the explosion or impact intoelectrical energy.

The following calculated example illustrates the concept in more detail.

Case 1. Conventional Supercapacitor

Determine the energy stored in a conventional supercapacitor, wherethere is a pair of current collectors with area a. There are twoelectrodes with high surface area (area A>>a) metal foams, which holdcharges +Q and −Q, which are then counter-balanced by charges −Q and +Qwhich originate from the liquid electrolyte.

Calculate the fields, voltages, and energy stored in the system

$\left. {\left. {\left. {\left. {\left. {{For}\mspace{14mu}{Region}\mspace{14mu} 1} \right){E_{1} = {{\frac{2\pi Q}{a} - \frac{2\pi Q}{a} + \frac{2\pi Q}{a} - \frac{2\pi Q}{a}} = 0}}{{For}\mspace{14mu}{Region}\mspace{14mu} 2}} \right){E_{2} = {{{- \frac{2\pi Q}{A}} - \frac{2\pi Q}{A} + \frac{2\pi Q}{A} - \frac{2\pi Q}{A}} = {- \frac{4\pi Q}{A}}}}{{For}\mspace{14mu}{Region}\mspace{14mu} 3}} \right){E_{3} = {{{- \frac{2\pi Q}{a}} + \frac{2\pi Q}{a} + \frac{2\pi Q}{a} - \frac{2\pi Q}{a}} = 0}}{{For}\mspace{14mu}{Region}\mspace{14mu} 4}} \right){E_{4} = {{{- \frac{2\pi Q}{A}} + \frac{2\pi Q}{A} - \frac{2\pi Q}{A} - \frac{2\pi Q}{A}} = {- \frac{4\pi Q}{A}}}}{{For}\mspace{14mu}{Region}\mspace{14mu} 5}} \right)$$E_{5} = {{{- \frac{2\pi Q}{a}} + \frac{2\pi Q}{a} - \frac{2\pi Q}{a} + \frac{2\pi Q}{a}} = 0}$

We will define the following quantitiesC ₀ =a/4πLC ₁ =A/4πδ

The voltage at the bottom current collector is assumed to be zero. Thevoltage at the top of region 2 is given by

$V = {{\left( \frac{4\pi\; Q}{A} \right)\delta} = \frac{Q}{C_{1}}}$

The voltage at the top of region 3 is given by

$V = {{\left( \frac{4\pi\; Q}{A} \right)\delta} = {{\frac{4\pi\; Q}{A}\delta} = \frac{Q}{C_{1}}}}$

The voltage at the top of region 4 is then given by

$V = {{{\left( \frac{4\pi\; Q}{A} \right)\delta} + {\left( \frac{4\pi\; Q}{A} \right)\delta}} = {{\frac{8\pi\; Q}{A}\delta} = {2\frac{Q}{C_{1}}}}}$

The energy stored in the system is given by

${Energy} = {{\frac{1}{2}{QV}} = {{\frac{Q}{2}\left( \frac{4\pi Q}{A} \right)\delta} - {\frac{Q}{2}\left\lbrack {\left( \frac{4\pi Q}{A} \right)\delta} \right\rbrack} + {\frac{Q}{2}\left\lbrack {{\left( \frac{4\pi Q}{A} \right)\delta} + {\left( \frac{4\pi Q}{A} \right)\delta}} \right\rbrack}}}$$\mspace{20mu}{{Energy} = {{{Q\left( \frac{4\pi Q}{A} \right)}\delta} = {Q^{2}C_{1}}}}$

Case 2. This Invention

Determine the energy stored in a partially modified supercapacitor,where there is a pair of current collectors with area a, holding chargeq. There are two electrodes with high surface area (area A>>a) metalfoam, which hold charges +Q and −Q, which are then counter-balanced bycharges −Q and +Q which originate from the liquid electrolyte. Thisdevice configuration can be created by mechanically driving the liquidelectrolyte partially out of the system.

Calculate the fields, voltages, and energy stored in the system

$\left. {\left. {{\left. {\left. {\left. {{For}\mspace{14mu}{Region}\mspace{14mu} 1} \right){E_{1} = {{\frac{2\pi Q}{a} - \frac{\pi Q}{a} + \frac{\pi Q}{a} - \frac{2\pi Q}{a}} = 0}}{{For}\mspace{14mu}{Region}\mspace{14mu} 2}} \right){E_{2} = {{{- \frac{2\pi Q}{A}} - \frac{\pi\; Q}{A} + \frac{\pi\; Q}{A} - \frac{2\pi Q}{A}} = {- \frac{4\pi Q}{A}}}}{{For}\mspace{14mu}{Region}\mspace{14mu} 3}} \right){E_{3} = {{{- \frac{2\pi Q}{a}} + \frac{\pi\; Q}{a} + \frac{\pi\; Q}{a} - \frac{2\pi Q}{a}} = {- \frac{2\pi\; Q}{A}}}}}{{For}\mspace{14mu}{Region}\mspace{14mu} 4}} \right){E_{4} = {{{- \frac{2\pi Q}{A}} + \frac{\pi\; Q}{A} - \frac{\pi\; Q}{A} - \frac{2\pi Q}{A}} = {- \frac{4\pi Q}{A}}}}{{For}\mspace{14mu}{Region}\mspace{14mu} 5}} \right)$$E_{5} = {{{- \frac{2\pi Q}{a}} + \frac{\pi\; Q}{a} - \frac{\pi\; Q}{a} + \frac{2\pi Q}{a}} = 0}$

We will define the following quantitiesC ₀ =a/4πLC ₁ =A/4πδ

The voltage at the bottom current collector is assumed to be zero. Thevoltage at the top of region 2 is given by

$V = {{\left( \frac{4\pi Q}{A} \right)\delta} = \frac{Q}{C_{1}}}$

The voltage at the top of region 3 is given by

$V = {{{\left( \frac{4\pi\; Q}{A} \right)\delta} + {\left( \frac{2\pi\; Q}{a} \right)\left( {L - {2\delta}} \right)}} = {{{\frac{4\pi\; Q}{A}\delta} + {\frac{2\pi\; Q}{a}\left( {L - {2\delta}} \right)}} = {\frac{Q}{C_{1}} + {\frac{Q}{2C_{0}}\left( {1 - {2{\delta/L}}} \right)}}}}$

The voltage at the top of region 4 is then given by

$V = {{{\left( \frac{4\pi\; Q}{A} \right)\delta} + {\left( \frac{2\pi\; Q}{a} \right)\left( {L - {2\delta}} \right)} + {\left( \frac{4\pi\; Q}{A} \right)\delta}} = {{2\frac{Q}{C_{1}}} + {\frac{Q}{2C_{0}}\left( {1 - {2{\delta/L}}} \right)}}}$

The energy stored in the system is given by

${Energy} = {{\frac{Q}{4}\left\lbrack \frac{Q}{C_{1}} \right\rbrack} - {\frac{Q}{4}\left\lbrack {\frac{Q}{C_{1}} + {\frac{Q}{2C_{0}}\left( {1 - {2{\delta/L}}} \right)}} \right\rbrack} + {\frac{Q}{2}\left\lbrack {{2\frac{Q}{C_{1}}} + {\frac{Q}{2C_{0}}\left( {1 - {2{\delta/L}}} \right)}} \right\rbrack}}$$\mspace{20mu}{{Energy} = {\frac{Q^{2}}{C_{1}} + {\frac{Q^{2}}{8C_{0}}\left( {1 - {2{\delta/L}}} \right)}}}$

Assume the metal foam has surface area of 100 m²/g and density of 1g/cm³. Assume the separation between charges in the metal foam is 10 nmon average

The electrode area is 1 cm² with separation 0.1 cm. Assume foamthickness of 10 microns.

The foam has volume 10⁻³ cm³, so A=0.1 m²=1000 cm²C ₀=1cm ²/4π(0.1cm)=10/4πcmC ₁=1000cm ²/4π10 nm=10⁹/4πcm

So C₁=10⁸C₀ This shows why supercapacitors have become a preferreddevice for storing charge.

So if we take a device where C₁=1F, and place 1.25V across it, Q=1.25 C.Because of the two capacitance layers, the full device would be rated asa 0.5F capacitor, and the voltage across the device would be 2.5V. Theenergy stored in this device would be 1.56 J.

If we assume we removed the half the charge from the middle layers, thetotal energy now would be more than 19 MJ, a more than 10⁷ increase inenergy.

This large increase in stored energy is conversion of mechanical energyused to remove charge in the form of the electrolyte from the system.

Electromagnetic Armor

The deployment of electromagnetic armor and other energy weaponsrequires power sources able to provide current pulses greater than 10 kAfor durations of tens of microseconds. Traditional metallic armorfunctions by dissipating the energy of a threat through localizedplastic work within the metal. Composite armor dissipates energy throughdelamination of the fiber from the resin and back-face deformation.However, both these approaches have been challenged to defeat the threatassociated with explosively formed penetrators (EFP).

Electromagnetic armor has been of high interest as a new approach tocountering the threat from EFPs. Electromagnetic armor looks to apply alarge electric current to the EFP. The forces applied to the EFP by thecurrent, and the heat generated by the current flow, act to speed theseparation of the penetrator into smaller particles, which pose a lesserthreat.

One of the limitations of electromagnetic armor is the need to providelarge currents (>20 kA) at any point of the armor. This historically hasrequired using large capacitor banks that are charged to voltages above10,000V. This voltage poses an extreme safety hazard to test personnel,and would be very challenging to implement in the field. Additionally,the response of the current to the EFP becomes dominated by theinductance of the cables connecting the capacitor bank to the armor. Ina real world system, it would be very challenging to have a singlecapacitor bank supply power to the armor for a large vehicle withoutweight of the cabling becoming unmanageable.

A key component to this concept is understanding that althoughelectromagnetic armor requires very large currents, these currents areactive for times on the order of tens of microseconds. This implies thatthe total charge required to power the system, Q, is actually not large.As an example, if a current of 50 kA flows for 100 microseconds, thetotal charge is only 5 C.

A modified version of this invention can be applied to powerelectromagnetic armor, as part of the armor itself. The basicconfiguration of the armor is shown in FIG. 3. Advantageously, theelectrochemical cell can be directly incorporated between two armorpanels, and no heavy cabling is required to carry the current to thearmor plates. Instead, the distortion of the armor plate by the EFP actsto generate the free current and voltage needed to defeat the EFP.

In this concept, two armor panels that are separated by a pair ofsupercapacitors that share a common cathode current collector. Theoperation of the armor occurs in several steps:

-   -   1) When the conductor strikes the outer armor panel, the panel        is deflected inwards while also being penetrated.    -   2) The deflection of the panel results in crushing the metal        foam electrodes    -   3) Crushing the electrodes ejects charged electrolyte from the        electrodes and results in a large net charge and large potential        difference between the electrodes    -   4) When the conductive threat reaches the second electrode, a        large current will flow through the conductor.    -   5) As the conductive threat continues to penetrate the armor,        the second pair of electrodes also become crushed, resulting in        large net charge and voltage.    -   6) When the conductive threat reaches the back electrode,        current will also flow between the second pair of electrodes.    -   7) If the first pair of electrodes and second pair of electrodes        are arranged perpendicular to each other, the change in current        insertion point will speed degradation of the threat.

Advantages of the present invention may include: the first is thatenergy is extracted from the threat to create the net charge and voltageon the supercapacitor electrodes, and the amount of energy that isremoved from the threat could be significant; second, the incorporationof the potential energy source within the armor plates eliminates theneed for a large external power source that must be connected to thearmor via large, heavy cables; the elimination of the cabling reducesthe inductance of the system, allowing the large currents to rise muchmore rapidly than is possible in conventional electromagnetic armor;third, the system, when in its charged, operational state, can becharged to 10V or less, for example only charged to about 2.5V, and thisvoltage is on the interior electrode in the paired supercapacitordevices; fourth, modulation of the current can be intrinsicallyincorporated into the armor through the use of perpendicular electrodes.

As another aspect to this invention, there may be potential to use thissame mechanism as a means to remove kinetic energy from projectiles. Inthis concept, the projectile striking one current collector would causethe foam to start to collapse. As this collapse begins to drive theelectrolyte from the foam, there is increased resistance to theprojectile, as increasing collapse of the foam causes increasing removalof the charged electrolyte. The invention also includes this method. Theenergy stored in this system scales as the amount of displaced chargesquared, so the total energy in the system increases rapidly.

As a comparative example, a 8kg projectile, traveling a 2 km/s(representative of the primary armament on a tank), has kinetic energyof 16 MJ, less than the energy required to drive the charging of thecapacitor in the previous example. Thus it may be possible to use thedisplacement of a charged fluid from a charged metal foam as a method toremove the kinetic energy from projectiles with less mass than requiredfor more conventional armor approaches.

Experimental Results

The first step in demonstrating the concept is to fabricate devices thatcan be crushed. The starting point was a porous Ni metal foam that was97% porous. Testing showed the foam could be easily crushed to 25% orless of its original thickness just applying relatively light pressure.

EXAMPLE 1

Two 1 cm×1 cm samples of the Ni foam were soaked in 1M KOH then placedon either side of a Celgard 3400-CD sample to form a capacitor. Thedevice was kept in a solution of 1M KOH. The device was charged at 1 mAto 1.0V, then discharged at a rate of 1 mA. The device discharged in 50seconds, indicating the device capacity was 50 mC. Results from thedevice are shown in FIG. 9.

EXAMPLE 2

Two 1 cm×1 cm samples of the Ni foam were soaked in 1M KOH then placedon either side of a piece of polycarbonate sheet to form a capacitor.The electrodes and separator were kept in a solution of 1M KOH. Thedevice was charged at 1 mA to 1.0V, then discharged at a rate of 1 mA.The device discharged in 55 seconds, indicating the device capacity was55 mC. Charge-discharge results from the device are shown in FIG. 10.

The device was charged to 1.0V, then moved onto a flat surface, andreconnected to measure the voltage. The voltage of the device wasobserved to decrease in a steady, monotonic manner, due to theself-discharge of the device. Approximately 50 seconds afterre-connection, the device was then struck by a three pound hammer. Thevoltage was observed to immediately increase by approximately 0.3V, andelectrolyte was observed to eject from the device. The voltage of thedevice then decreased in a manner consistent with the priorself-discharge. After approximately 40 seconds, the device was struckagain. This impact resulted in a much smaller increase in voltage, andthe self-discharge after the second impact changed in shape. The devicewas impacted a third and fourth time, with progressively smaller jumpsin voltage, and more rapid self-discharge. Little electrolyte wasobserved to eject from the device after the first impact.

Additional example devices were fabricated and showed similar behaviorto that observed in FIG. 9 and FIG. 10.

EXAMPLE 3 Control Tests

To demonstrate that the results in FIG. 11 were due to the proposedmechanism, two control tests were performed. In the first test, a devicewas fabricated as in the previous example, but was not charged. Thedevice was placed onto a flat surface, then impacted with a three poundhammer, at approximately the same speed as in the previous example. Theresults of this test are given in FIG. 12. As can be seen, the devicewhich had not been charged showed minimal change in voltage upon impact,even though similar amount of electrolyte was seen to eject from thedevice upon impact. This result is consistent with the proposedmechanism.

In the second control test, a device was fabricated as in the previoustests, but no electrolyte was introduced into the device. The device wasplaced onto a flat surface, then impacted with a three pound hammer asbefore. The results of this test are shown in FIG. 13. As can be seenfrom the figure, the voltage of the device is not stable, with itchanging in response to a range of environmental conditions. The erraticbehavior of the voltage of the device indicates there is effectively nocharge associated with the voltage change. This is expected, as theeffective capacitance of the device with no electrolyte is on the orderof pico farad or smaller.

EXAMPLE 4 Drop Tower Testing

In this example, several devices were fabricated as in the previousexamples. The devices were charged to 1.0V, then placed onto the stageof a drop tower. A weight was then dropped onto the device from a fixedheight, and the increase in the voltage due to impact recorded. FIG. 14shows the increase in voltage as a function of the drop height. The datasuggests there may be an increase in voltage with drop height, althoughthere is enough scatter in the data to make analysis challenging.Several additional tests were performed but not recorded, as the impactresulted in sufficient damage to the device to prevent recording thevoltage spike.

EXAMPLE 5 Alternate Electrode Materials

In this example, a device was fabricated using a carbon nanotube (CNT)film as the porous electrodes. The CNT films had high porosity and highsurface area. The device was measured to have capacity of 0.25 mC, asshown in FIG. 15. When this device was tested using the drop tower,there was no increase in the voltage due to the impact. In fact, in thiscase, the voltage was seen to drop. After the test was complete, thedevice was examined, and it was found that the CNT film fractured. It isfelt this is the cause of the voltage decrease upon impact.

What is claimed:
 1. An armor panel, comprising in sequence: a firstarmor plate, an anode, a first electrolyte, a porous insulatingseparator, a second electrolyte, a cathode, and a second armor plate;and an electrical connection between the anode and cathode; and furthercomprising at least one outlet for the first electrolyte and the secondelectrolyte; and wherein the components are connected such that, when akinetic or conductive threat impacts or travels through an armor plate,the first and second electrolyte are ejected and a potential betweencathode and anode is increased.
 2. The armor panel of claim 1 comprisingtwo anodes so that the cathode could be isolated in the interior of thedevice.
 3. The armor panel of claim 1 wherein the cathode is shared witha second anode and further comprising a third electrolyte, a secondporous insulating separator, a fourth electrolyte; all disposed betweenthe first and second armor plates.
 4. A method of reducing a conductiveor kinetic threat using the armor panel of claim 1.